This type of chip resistor is provided with a ceramic substrate, a pair of front electrodes, a resistor body, a protective layer, a pair of back electrodes, a pair of end-surface electrodes, and a pair of external electrodes. The ceramic substrate is shaped like a cuboid. The pair of front electrodes are provided on lengthwise opposite end portions of a front surface of the ceramic substrate. The resistor body is provided on the front surface of the ceramic substrate so as to be connected to the pair of front electrodes. The protective layer is provided so as to cover the resistor body. The pair of back electrodes are provided on lengthwise opposite end portions of aback surface of the ceramic substrate. The pair of end-surface electrodes are provided on opposite end surfaces of the ceramic substrate so as to cover the front electrodes and the back electrodes. The pair of external electrodes are formed by plating treatment applied to external surfaces of the end-surface electrodes.
The chip resistor configured thus is surface-mounted on a circuit board in the following manner. That is, after a soldering paste is printed on lands provided in the circuit board, the back electrodes are made to face downward and the external electrodes are placed on the lands. In this state, the soldering paste is melted and solidified to thereby surface-mount the chip resistor on the circuit board. However, fatigue, cracks, fracture, etc. are apt to occur at solder bonding portions due to thermal stress.
To solve this problem, according to the background art, a chip resistor has been proposed, as disclosed in Patent Literature 1. The chip resistor has a configuration in which each of back electrodes is formed into a two-layer structure consisting of an inner layer made of sintered silver and an outer layer made of an electrically conductive resin (resin silver), and solder bonding is applied to external electrodes covering the back electrodes each having such a two-layer structure. In the chip resistor configured thus according to the background art, the outer layers of the back electrodes making contact with solder bonding portions on lands of a circuit board are made of the electrically conductive resin. Therefore, thermal stress acting on the solder bonding portions can be relaxed in comparison with a case where each of back electrodes is made of only sintered silver.
In addition, another chip resistor has been proposed, as disclosed in Patent Literature 2. The chip resistor has a configuration in which each of back electrodes is constituted by a first electrode layer made of sintered silver and a second electrode layer made of the sintered silver and laminated on the first electrode layer at a position separate from an edge portion of the first electrode layer, and solder bonding is applied to external electrodes covering such back electrodes. In the chip resistor configured thus according to the background art, a step is formed at a portion extending from a side surface of the second electrode layer to a front surface of the first electrode layer, and a step portion corresponding to the step is also formed in each of the external electrodes. Therefore, thicknesses of solder bonding portions can be increased by the step portions so that thermal stress can be relaxed.